The subject matter of the present invention pertains to means for converting a non-interlaced video signal, such as that produced by an information display system, into an interlaced form more compatible with a conventional television receiver.
In the field of information display, it is often convenient and advantageous to employ a non-interlaced video signal when producing a raster-scan image on, for example, the display screen of a cathode-ray tube. The use of such a signal, repeated at a frame rate equal to the interlaced field rate, permits the production of high-resolution graphic images without the flicker inherent in those parts of an interlaced image defined by a single point or a single horizontal line. Non-interlaced signals are also advantageous for producing permanent copies of a displayed image.
A problem occurs when it is desired to display a non-interlaced image simultaneously on both a high-resolution, high-bandwidth graphics device and a low-resolution, low-bandwidth monitor such as, for example, the aforementioned television receiver. In such a case, the non-interlaced signal must be converted to its interlaced equivalent before being transmitted to the lower bandwidth monitor. Depending on the particular monitor employed, it may also be necessary to make certain timing adjustments; for example, to convert from U.S. standards to European standards.
Known systems for converting a non-interlaced signal to interlaced form include those disclosed by Bockwoldt U.S. Pat. No. 3,947,826 and de Niet U.S. Pat. No. 3,832,487. In Bockwoldt, a non-interlaced video signal produced by successively scanning a pair of infrared detectors is transformed into alternating fields of interlaced lines by storing parallel channel data, one line-set at a time, in preselected storage devices and then reading the data out in a manner producing the desired interlaced signal. In de Niet, a non-interlaced signal from a television camera is converted to interlaced form by separating each frame of the signal into two fields, writing both fields into a storage device, and then reading the information back out in field sequence. The Bockwoldt system performs its transformation on a line-by-line basis, while the de Niet system operates on an entire frame of input information.
A disadvantage of the Bockwoldt system is that its interlaced signal contains two copies of each input scan line, a rather unconventional arrangement and one not readily applicable to the field of information display. A disadvantage of the de Niet system is that it requires a storage device capable of storing a full frame of image information. The de Niet system also requires its input and output devices, the camera and monitor, respectively, to have essentially the same bandwidths.